[cfe-commits] [PATCH] Support for universal character names in identifiers

Jordan Rose jordan_rose at apple.com
Fri Jan 18 11:40:43 PST 2013

On Jan 18, 2013, at 11:36 , Richard Smith <richard at metafoo.co.uk> wrote:

> On Fri, Jan 18, 2013 at 11:20 AM, Jordan Rose <jordan_rose at apple.com> wrote:
>> On Jan 17, 2013, at 17:43 , Richard Smith <richard at metafoo.co.uk> wrote:
>>> On Thu, Jan 17, 2013 at 11:31 AM, Jordan Rose <jordan_rose at apple.com> wrote:
>>>> How about this approach?
>>>> - LexUnicode mirrors LexTokenInternal, dispatching to the proper lex method based on the first Unicode character in a token.
>>>> - UCNs are validated in readUCN (called by LexTokenInternal and LexIdentifier). The specific identifier restrictions are checked in LexUnicode and LexIdentifier.
>>>> - UCNs are recomputed in Preprocessor::LookUpIdentifierInfo because we start with the spelling info there, but all the validation has already happened.
>>> This seems reasonable to me. It looks like this will now correctly reject
>>> #if 0
>>> \u0000
>>> #endif
>>> ... which I believe the old approach accepted.
>>>> With these known flaws:
>>>> - the classification of characters in LexUnicode should be more efficient.
>>>> - poor recovery for a non-identifier UCN in an identifier. Right now I just take that to mean "end of identifier", which is the most pedantically correct thing to do, but it's probably not what's intended.
>>>> - still needs more tests, of course
>>>> FWIW, though, I'm not sure unifying literal Unicode and UCNs is actually a great idea. The case where it matters most (validation of identifier characters) is pretty easy to separate out into a helper function (and indeed it already is). The other cases (accepting Unicode whitespace and fixits for accidental Unicode) only make sense for literal Unicode, not escaped Unicode.
>>> For build systems which automatically convert UTF-8 to UCNs for gcc
>>> compatibility[0], it's not implausible that UCN-encoded smart quotes
>>> or whitespace might end up in Clang input.
>>> [0]: http://gcc.gnu.org/wiki/FAQ#utf8_identifiers
>>>> Anyway, what do you think?
>>> Generally, I like this. Some specific comments:
>>> In readUCN, \u123 isn't an error, it's two separate tokens. Perhaps
>>> the diagnostics here should be warnings instead?
>> Since a lone backslash always produces an invalid token, it seems reasonable to leave these as errors, but yes, I now need to go back and not consume anything in that case.
> The issue is that it's not an invalid token at this phase of
> translation. If the preprocessing-token is not converted to a token,
> it's not an error. For instance, it might be skipped in a #if 0, or it
> might be stringized, or it might be in a macro which is never
> expanded.

*sigh* Right. Warnings it is.

>>> Likewise, in LexIdentifier and LexTokenInternal, you shouldn't call
>>> ConsumeChar until you know that you have actually got a UCN.
>>> Likewise, in LexUnicode, err_non_ascii can be at most a warning; we're
>>> required to produce a preprocessing-token for each character which
>>> can't be the start of another token. The err_invalid_utf8 part in
>>> LexTokenInternal is fine though, since that's covered by the
>>> implementation-defined mapping from physical source file characters to
>>> the basic source character set.
>> *sigh* This seems like more justification to distinguish UCNs and actual Unicode to handle the "accidental" case, but I will make sure UCNs as written never fall into that block. (Actually, I'll just go with your way for now and handle that QoI issue later.)
> One thing I missed before: please don't use iscntrl or isxdigit;
> they're dependent on the current locale (and to be safe, don't use
> isascii either).

I understand for iscntrl, but isascii appears a lot and the expanded form is ugly. I guess I'll write my own wrapper.


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